The invention relates to a fuel injection system for a Diesel engine which includes a high pressure fuel pump supplying fuel under pressure to a common-rail fuel supply conduit which is in communication with valve-controlled injectors fop the injection of fuel under the control of an electronic control unit.
Such a fuel injection system with a high pressure pump and a common supply conduit for all injectors and control elements which can be activated to cause opening of the injector needle valve is known from the publication ATZ/MTZ special edition Motor and Environment '92 "Electronic Controlled Fuel Injection System for Clean Diesel Engine", pages 28-30 by Toshihiko Omari: As control element an electromagnet is used for operating a 3-way valve which normally provides for high pressure communication between the supply conduit and the backside of the injector needle of an injector with a bore type injection orifice but which, in operative position with activated control element, provides for pressure relief communication between the backside of the injector needle and a fuel discharge conduit to permit opening of the injector needle.
With such so-called Common-Rail-System fuel injection arrangements the fuel pressure level which can be freely chosen affects directly the injection time. An excessively high injection pressure will, with small injection amounts, necessarily result in short injection times which however is not desirable and even problematic with today's powerful, and especially with highly charged, direct-injection Diesel engines.
It is therefore the object of the present invention to provide a fuel injection system of the type referred to above, wherein the injection time can be selected over the whole engine performance range for each individual load point independently of the level of the fuel injection pressure.